Medications come from manufacturers and wholesalers who have safety stock, and when it's short-dated, they destroy it.
药物来自有安全库存的制造商和批发商， 当它过期时，他们会销毁它。
英语百科
Safety stock
Safety stock (also called buffer stock) is a term used by logisticians to describe a level of extra stock that is maintained to mitigate risk of stockouts (shortfall in raw material or packaging) due to uncertainties in supply and demand. Adequate safety stock levels permit business operations to proceed according to their plans. Safety stock is held when there is uncertainty in demand, supply, or manufacturing yield; it serves as an insurance against stockouts.